1. Field of the Invention
This invention relates in general heat exchangers for use in motor vehicle air conditioning systems having compression fittings, and in particular to a heat exchanger having a compression fitting which includes a tubing connector formed of materials which may be run through a brazing furnace for brazing to other components of the heat exchanger.
2. Description of the Prior Art
Prior art motor vehicle heat exchangers, such as condensers, have been fabricated by forming various condenser components of aluminum alloy materials having a brazing clad. In one type of heat exchanger, these components include two header tanks which are aligned in a parallel arrangement, flow tubes which extend in parallel between the two header tanks, and fins which are placed between the tubes for enhancing the heat transfer capacity of the flow tubes. These various condenser components are typically assembled and secured to an assembly fixture to form a condenser brazing assembly, which is run through a brazing furnace to sealingly secure the various condenser components together.
Frame elements, brackets and some refrigerant flow connectors, for passing refrigerant to and from the condenser, are also included in the condenser assembly and run through the brazing furnace. However, some types of prior art refrigerant flow connectors cannot be passed through the brazing furnace without threatening the integrity of the seal they are intended to provide. One such type of prior art flow connectors includes "tube-o" connectors used in compression fittings for connecting refrigerant flow lines to the condenser, such as for passing refrigerant from the system compressor to the condenser. A tube having a tube-o connector for connecting a condenser to a refrigerant flow line is brazed to the condenser as a separate assembly step which occurs after the condenser assembly is passed through the brazing furnace.
Prior art tube-o connectors are typically formed on tubes which are made from an aluminum alloy. A rib is formed into the tube, close to an outer end of the tube, with the rib an integral part of the tube. A pilot portion of the tube extends between the rib and the outer end of the tube. The rib includes two opposite, substantially parallel sides, an outer side and an inner side. The outer side of the rib is herein defined as the side of the rib closest to the outer end of the tube to which the refrigerant flow line is connected, and the inner side of the rib is herein defined as the side of the rib from which the tube extends to connect to the condenser.
A compression fitting incorporating a tube-o connector typically includes a female tubing connector, a male tubing connector, and an annular seal member, such as an elastomeric o-ring. The female tubing connector is placed around a portion of the tube which is to extend between the rib and the condenser. The male tubing connector is sealingly secured to the end of a refrigerant flow line to be connected to the tube. The annular seal member is placed around the pilot end of the tube, next to the rib. The male and female tubing connectors are threaded for coupling together, and squeezing the rib and annular seal member together with a compression load.
The female tubing connector includes a shoulder for pressing against the inner side of the rib to both locate the female tubing connector with respect to the outer end of the tube, and to apply the compression load to the rib. The male tubing connector presses against the annular seal member. The compression fitting is made up by screwing the female and male tubing connectors together, to press the annular seal member and the rib together with the compression load. This squeezes the annular seal member between the rib, the tube and the male tubing connector to seal between the tube and the refrigerant flow line.
The sealing integrity of a tube-o connector for use in this type of compression fitting is compromised when passed through a brazing furnace. The tube-o connector is typically formed from an aluminum alloy. Prior to passing through the brazing furnace, the tube-o connector has been hardened by methods determined according to the alloy selected to improve the mechanical strength of the aluminum alloy. These methods include solution hardening, age hardening, work hardening and other appropriate methods. After passing through the brazing furnace, the aluminum alloy is annealed which reduces the mechanical strength of the aluminum alloy. The tube-o connector becomes too soft and ductile for the female tubing connector to press against during makeup with the male tubing connector.
Passing the shoulder of the female tubing connector along the inner side of the rib of a softened tube-o connector will often result in galling and gouging of the rib. This results in deformation of the entire rib, which destroys the sealing integrity of the tube-o connector. Thus, an extra assembly step is required to braze a tube having a prior art tube-o connector to a condenser after the condenser is passed through a brazing furnace.